GB1046722A - Process for preparing surface-treated pigments - Google Patents

Abstract

A process for producing surface-treated pigments having an organophilic surface layer and being suitable for use in organic solvents, lacquers and synthetic resins comprises the following steps:- (I) forming a dispersion of the pigment in water, and subsequently (II) adding an aqueous solution of an alkali metal complex salt, an alkali metal borate or boric acid, and subsequently either (III) adding an acqueous solution of a water-soluble salt of a di-, tri- or tetravalent metal and (IV + ve) where the pigment has a positive surface charge, adding an aqueous solution of an alkali metal salt or ammonium salt of an acidic auion-active agent, or (IV - ve) where the pigment has a negative surface charge, adding an aqueous solution of a water-soluble salt of a cation-active -onium or -inium organic base, or performing steps III and IV in the reverse order, and subsequently (V) separating the pigment from the aqueous solution/suspension. "Alkali metal complex salts" is defined as reaction products of alkali metal compounds with oxides or hydroxides of amphoteric character, e.g. zincates, aluminates, arsenites, arsenates, antimonites, antimonates, stannates, plumbites and chromites. Many examples of surfactants and polyvalent metal salts are given. The charge on the particles depends on which reagent was in excess when the pigment was precipitated, or upon the relative potentials of anion and cation. The process may be applied to single substances such as TiO2, Fe2O3, Pb3O4, Cr2O3, BaSO4, CaS, ZnS, sulphides of mercury, antimony, arsenic and tin or cobalt violet (Co3(PO4)2; to organic pigment such as phthalocyanines and azopigments; to mixed pigments such as cadmium sulphide-selinide and lithopone; and to natural products such as bauxite red and ultramarine.ALSO:A process for producing surface-treated pigments having an organophilic surface layer and being suitable for use in organic solvents, lacquers and synthetic resins comprises the following steps: (I) forming a dispersion of the pigment in water, and subsequently (II) adding an aqueous solution of an alkali metal complex salt, an alkali metal borate or boric acid, and subsequently either (III) adding an aqueous solution of a water-soluble salt of a di-, tri- or tetravalent metal and (IV + ve) where the pigment has a positive surface charge, adding an aqueous solution of an alkali metal salt or ammonium salt of an acidic anion-active agent, or (IV - ve) where the pigment has a negative surface charge, adding an aqueous solution of a water-soluble salt of a cation-active -onium or -inium organic base, or performing steps III and IV in the reverse order, and subsequently (V) separating the pigment from the aqueous solution/suspension "Alkali metal complex salts" is defined as reaction products of alkali metal compounds with oxides or hydroxides of amphoteric character, e.g. zincates, aluminates, arsenites, arsenates, antimonites, antimonates, stannates, plumbites and chromites. Many examples of surfactants and polyvalent metal salts are given. The charge on the particles depends on which reagent was in excess when the pigment was precipitated, or upon the relative potentials of anion and cation. The process may be applied to single substances such as TiO2, Fe2O3, Pb3O4, Cr2O3, BaSO4, CaS, ZnS, sulphides of mercury, antimony, arsenic and tin or cobalt violet (Co3(PO4)2); to organic pigments such as phthalocyanines and azo-pigments; to mixed pigments such as cadmium sulphide-selinide and lithopone; and to natural products such as bauxite red and ultramarine.